WASHINGTON - Electronic flaws weren't to blame for the reports of sudden, unintended acceleration that led to the recall of thousands of Toyota vehicles, the government said Tuesday.

Some of the acceleration cases could have been caused by mechanical defects - sticking accelerator pedals and gas pedals that can become trapped in floor mats - that have been dealt with in recalls, the government said.

And in some cases, investigators suggested, drivers simply hit the gas when they meant to press the brake.

"We feel that Toyota vehicles are safe to drive," declared Transportation Secretary Ray LaHood.

The investigation bolstered Toyota's contentions that electronic gremlins were not to blame and its series of recalls - involving more than 12 million vehicles globally since fall 2009 - had directly addressed the safety concerns.

Transportation officials, assisted by engineers with NASA, said the 10-month study of Toyota vehicles concluded there was no electronic cause of unintended high-speed acceleration. The study, launched at the request of Congress, responded to consumer complaints that flawed electronics could be the culprit behind complaints that led to Toyota's spate of recalls.

Recalls to fix sticking accelerator pedals, gas pedals that became trapped in floor mats, and other safety issues have posed a major challenge for the world's No. 1 automaker, which has scrambled to protect its reputation for safety and reliability. Toyota paid the U.S. government a record $48.8 million in fines for its handling of three recalls.

Toyota said the report should "further reinforce confidence in the safety of Toyota and Lexus vehicles" and "put to rest unsupported speculation" about the company's electronic throttle control systems, which are "well-designed and well-tested to ensure that a real world, un-commanded acceleration of the vehicle cannot occur."

Toyota reported a 39 percent slide in quarterly profit earlier Tuesday but raised its full-year forecasts for earnings and car sales. The financial results and government report boosted shares of the automaker on Wall Street by more than 4 percent, to close at $88.57.

Analysts said the report would help Toyota's reputation but the company would still need to work hard to regain its bulletproof image of reliability. Toyota was the only major automaker to see a U.S. sales decline last year at 0.4 percent.

"This is really something that is going to take years and years to recover," said Rebecca Lindland, director of automotive research with consulting firm IHS Automotive.

Federal officials said they thoroughly examined the acceleration reports and could not find evidence of an electronic problem. Instead, investigators with the National Highway Traffic Safety Administration said the evidence showed that cases in which owners complained about ineffective brakes were most likely caused by "pedal misapplication," in which the driver stepped on the accelerator instead of the brakes.

Many of the complaints involved cases in which the vehicle accelerated after it was stationary or at very low speed.

LaHood said NASA engineers "rigorously examined" nine Toyotas driven by consumers who complained of unintended acceleration. NASA reviewed 280,000 lines of software code to look for flaws that could cause the acceleration. Investigators tested mechanical components in Toyotas that could lead to the problem and bombarded vehicles with electro-magnetic radiation to see whether that could make the electronics cause the cars to speed up.

Electronic problems can include buggy software, circuitry influenced by electrical interference and electrical shorts. The problems are often difficult to spot and can surface when combined with environmental factors like a blast from a heater vent or moisture from the road.

A preliminary part of the study, released last August, failed to find any electronic flaws based on a review of event data recorders, or vehicle black boxes.

Not everyone was convinced. Rhonda Smith, of Sevierville, Tennessee, who last year testified before a congressional committee that her Lexus raced up to 100 miles per hour without her control, said Tuesday there had to be a cause other than floor mats or sticky gas pedals because she said neither happened in her case.

"There is a defect in that car whether they want to believe it or not," Smith said. "They need to keep searching."

NHTSA administrator David Strickland, however, told reporters that the agency conducted extensive tests on Smith's vehicle and found "no other vulnerabilities" beyond trapped floor mats.

Consumer advocates and safety groups have raised concerns that flawed electronics could be causing unwanted acceleration in the Toyotas. They have questioned the reliability of the event data recorders studied by the government, saying they could be faulty or fail to tell the whole story of the individual crashes.

Joan Claybrook, a former NHTSA administrator who previously led consumer group Public Citizen, said the government investigation discounted research conducted by plaintiffs' attorneys.

"The facts are still quite substantial that there's a problem and I think they could have done a lot more in terms of gathering more expertise," Claybrook said.

To promote safety, LaHood said NHTSA was considering new regulations. They include requiring brake override systems on all vehicles, standardizing keyless ignition systems and requiring event data recorders, or vehicle black boxes, on all new vehicles.

Transportation officials said they would also consider conducting more research on electronic control systems and review the placement and design of accelerator and brake pedals.

Since the recalls, Toyota has installed brake override systems on new vehicles. The systems automatically cut the throttle when the brake and gas pedals are applied at the same time.

The company also created engineering teams to examine vehicles that are the subject of consumer complaints and appointed a chief quality officer for North America amid complaints its U.S. division did not play a large enough role in making safety decisions.

Toyota's safety issues received broad attention from the government after four people were killed in a high-speed crash involving a Lexus near San Diego in August 2009.

NHTSA has received about 3,000 reports of sudden acceleration incidents involving Toyota vehicles during the past decade, including allegations of 93 deaths. NHTSA has confirmed five of them.

Congress considered sweeping safety legislation last year that would have required brake override systems, raised penalties on auto companies that evade safety recalls and given the government the power to quickly recall vehicles. But the bills failed to win enough support.

The National Academy of Sciences is conducting a separate study of unintended acceleration in cars and trucks across the auto industry. The panel is expected to release its findings this fall.

AP Auto Writers Tom Krisher and Sharon Carty in Detroit contributed to this report.